Problem: $ { \left[\begin{array}{rrr}{2} & {3} & {-1} \\ {1} & {3} & {1}\end{array}\right]+\left[\begin{array}{rrr}{-1} & {0} & {0} \\ {-1} & {3} & {-1}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{2}+{-1} & {3}+{0} & {-1}+{0} \\ {1}+{-1} & {3}+{3} & {1}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{1} & {3} & {-1} \\ {0} & {6} & {0}\end{array}\right]}$